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Frame Geometry

Avit5Avit5 Posts: 114
edited August 2013 in Road buying advice
In mt earlier thread about 6800 & Di2 I stated that I had ruled out the likes of Canyon bikes due to me wanting a bike with a longer HT due to my long legs.(height 184cm and inseam of 93cm)
But.....just comparing the frame geometry on a Giant Defy to the Canyon Ultimate AL (ignore the carbon/alu debate at this stage).

Giant Defy - TT : 57.5 HT : 20.5 Wheel Base : 102.2 Head Angle : 72.5 Seat Angle : 73 Chain Stay : 420

Canyon AL - TT : 58.3 HT : 19 Wheel Base : 101.4 Head Angle : 73.25 Seat Angle : 73.5 Chain Stay : 410

So in theory if I was to specify a 10mm shorter stem on the Canyon AL would the TT be about the same ?
What effect do the Seat / Head Angles have on the TT length and the reach to the bars on each bike.
Also I know the HT is lower on the Canyon bike but initially I could flip the stem to raise it a little.

I only question this because if I can get say the Canyon to be roughly the same setup as a Defy then I can get a much better value bike than say a Trek or Giant. (I am only using the Canyon Al as an example - just if my theory works like I hope then it would bring other bikes into the equation).

Posts

  • CalpolCalpol Posts: 1,039
    In theory you are correct but, are you sure that you need a longer TT. I am 184cm also but with 85(ish)cm inseam. I wouldnt ride a bike with 583mm TT. I would be too stretched out. So unless you have really long arms maybe that Canyon would be too big for you.
    The Giant has slightly steeper seat angle so that will effect the TT length I think. FWIW if I was buying the Canyon I would be getting a 58. Its easier to make a small bike bigger than the other way, seems to be the general advice on here.
  • styxdstyxd Posts: 3,234
    Get a bike fit
  • tonye_ntonye_n Posts: 832
    styxd wrote:
    Get a bike fit
    This. ^^
  • MichaelWMichaelW Posts: 2,164
    Consider TT length in 2 parts:
    In front of the BB
    behind the BB
    When setting your saddle layback, you do so in relation to the BB (via the crank 3:00 position).
    No matter how much toptube you have behind the BB, you should have the same layback, just achieved via a different mix of angle, seapost clamp design and saddle rail position.
    The TT infront of the BB contributes to reach. If you have 2 frames, one with a slack seat-tube angle and one with a steep angle, then the slack one will have a shorter effective TT reach.

    A bike fit will set the points of contact for either of those 2 frame geometries but the balance and handling may differ.
    When you have a bike setup you like, you may have to transfer the points of contact positions to another frame of different angles.
  • rolf_frolf_f Posts: 16,015
    Long legs = short top tube, tall head tube. Look for bikes marketed as 'sportive'. If your legs are long enough (eg like mine) it can get quite tight to get a good fit (ie short top tube and short stem to enable reach to the bars resulting in knees getting very close to the bars when standing out of the saddle).

    PS - get a bike fit!
    Faster than a tent.......
  • Avit5Avit5 Posts: 114
    Thanks for all the replies chaps.
    Get the message about a bike fit - so do this before I purchase my next bike then ?
    My current bike (no idea if it is set up correctly as it was my first road bike) has TT of 56.7 and HT of 20.0.
    Now I am not uncomfortable on it and have managed several 100 miles sportives on it but do tend to be a bit upright compared to the others I ride with. Not that it matters as I am not uncomfortable. Maybe I have to accept with my body proportions / age / flexibility that I am never going to be low and stretched out on a bike.

    Rolf F - I have been looking at 'sportive' bikes like the Domane/Defy/Synapse but just thought I might be ok on something else. I have no problem with having any of the bikes on my list as I am sure I will never do them justice anyway! Out of interest what bike do you have ?
  • drlodgedrlodge Posts: 4,826
    Get a bike fit or via some other method, get your existing bike setup to establish the "proper fit". Once you have that you can understand the various dimensions you have and overlay those onto a new frame even with slightly different geometry. e.g. If the new frame has a steeper seat tube angle, the top tube will need to be a tad shorter for the same reach, and the seat post have more set back. Effective top tube length combined with seat tube angle, and head tube length are the key dimensions for me.
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  • Avit5Avit5 Posts: 114
    Looks like I do need to invest in a proper bike fit session. Suspect my current st up is at least nearly right though because if not then surely I would be experiencing aches and pains after a 100 miles. Like I say it just seems that i sit a bit upright in the saddle but that maybe just the correct position for me. My biggest problem i have found when trying 'new' bikes for size is the drop from saddle height to bars. On a Giant TCR that I tried in Large (58.5 TT & 18.5 HT) I had the saddle at such a high setting for my long legs that the drop seemed huge to the bars but no way could I get the XL in the TCR as I would not have been able to reach the bars ! Defo looks like I need a bike with higher HT so I think I am in the correct ballpark when looking at Defy & Domane bikes.
  • Camcycle1974Camcycle1974 Posts: 1,356
    How about a frame with more traditional geometry like a cannondale caad 8/10 or super 6? With long legs a compact frame Will always give you a big seat to bar drop if you get the right tt length. Sounds like you might be better suited to a non-compact frame.
  • Avit5Avit5 Posts: 114
    Camcycle1974 wrote:
    How about a frame with more traditional geometry like a cannondale caad 8/10 or super 6? With long legs a compact frame Will always give you a big seat to bar drop if you get the right tt length. Sounds like you might be better suited to a non-compact frame.

    But the Canyon AL is nearly the same measurements as the CAAD 10 but with a higher HT on the Canyon.
    So you are saying this might be a better fit than the defy or domane ?
  • Camcycle1974Camcycle1974 Posts: 1,356
    Avit5 wrote:
    Camcycle1974 wrote:
    How about a frame with more traditional geometry like a cannondale caad 8/10 or super 6? With long legs a compact frame Will always give you a big seat to bar drop if you get the right tt length. Sounds like you might be better suited to a non-compact frame.

    But the Canyon AL is nearly the same measurements as the CAAD 10 but with a higher HT on the Canyon.
    So you are saying this might be a better fit than the defy or domane ?

    It's possible. Just because the Defy/Domane are sold as comfortable endurance bikes it doesn't mean they will suit all body types or be comfortable for everyone. Struggled to get comfy on my Defy, hence why I am selling it. Long legs in comparison to my height.
  • Avit5Avit5 Posts: 114
    Camcycle - Have you decided on your next purchase then ? I have seen a few threads with you looking at Planet X.
    I presume the bikes you are now looking at have a shorter TT than the Defy then.
  • rolf_frolf_f Posts: 16,015
    Avit5 wrote:
    Rolf F - I have been looking at 'sportive' bikes like the Domane/Defy/Synapse but just thought I might be ok on something else. I have no problem with having any of the bikes on my list as I am sure I will never do them justice anyway! Out of interest what bike do you have ?

    I have a Ribble Gran Fondo, a Look 585 Optimum and a Scott CR1 frame that will probably eventually replace the Ribble. All bought because they fit me rather than (or despite!) because they happened to be described as 'sportive' bikes. The difference in folks geometry can be greater than the difference between a 'sportive' and 'normal' geometry frame so it is really all just marketing bull but the point is that the geometry characteristics of a sportive frame do tend to work for the long legged. Basically, my fit is racy on the sportive frame. If I actually wanted a sportive fit, I'd probably struggle!
    Camcycle1974 wrote:
    How about a frame with more traditional geometry like a cannondale caad 8/10 or super 6? With long legs a compact frame Will always give you a big seat to bar drop if you get the right tt length. Sounds like you might be better suited to a non-compact frame.

    The seat to bar drop won't be affected by whether or not the frame is compact (assuming by compact you mean slopey top tube). Infact, seat to bar drop shouldn't be affected by the bike at all if it actually fits. All a compact frame will do is give you a greater length of exposed seatpost than a non compact frame. Whether that matters is down to personal taste though I think really compact road bike frames look like MTBs! :lol: What does matter, simplistically, is head tube height and top tube length and, less simplistically, frame angles as well.
    Faster than a tent.......
  • gloomyandygloomyandy Posts: 520
    Take a look at the following artical:
    http://www.cervelo.com/en/engineering/t ... d-fit.html
    It will help you understand how TT is not really a very useful way to judge fit. Then try and get the best fit you can on your existing bike, measure the saddle position (set back and height from BB) and the reach and stack of your good position on your existing bike. Once you have that you should be able to work out if you can replicate this good position on any other bike....
  • randorando Posts: 285
    That's a very interesting article about geometry from Cervelo. But how would you calculate stack / reach from the geometry chart from this link
    http://www.vitusbikes.com/road-bikes-20 ... 3#geometry

    to my untrained eye this looks a really aggressive setup when you look at the HT lenghts (15.5 on the 58cm ). So if you could get the stack & reach figures it might not be that bad. I have read reviews on the vitus vitesse and none have ever mentioned it being an aggressive setup. I mention the vitus because at CRC currently you can get one with dura ace 9000 for £2300 which is stonking value.
    http://www.chainreactioncycles.com/vitu ... -prod81021
    But just on reading the geometry chart to me states very low front end.
  • giant_mangiant_man Posts: 6,878
    Avit5 wrote:
    Thanks for all the replies chaps.
    Get the message about a bike fit - so do this before I purchase my next bike then ?
    Well this the only way of knowing what to look for, dimensions wise, in your next frame surely.
  • Avit5Avit5 Posts: 114
    Any recommendations then for bike fit in the leicestershire area?
    Just looked at one in Warwickshire and they are fully booked till end of September. Blimey business must be good!!
  • 6wheels6wheels Posts: 411
    The seat to bar drop won't be affected by whether or not the frame is compact (assuming by compact you mean slopey top tube). Infact, seat to bar drop shouldn't be affected by the bike at all if it actually fits. All a compact frame will do is give you a greater length of exposed seatpost than a non compact frame. Whether that matters is down to personal taste though I think really compact road bike frames look like MTBs! :lol: What does matter, simplistically, is head tube height and top tube length and, less simplistically, frame angles as well.

    After looking at the geometry of the new Synapse(with its barmy head tube length), I've come to exactly the same conclusion.

    Nice post Rolf.
  • Camcycle1974Camcycle1974 Posts: 1,356
    Avit5 wrote:
    Camcycle - Have you decided on your next purchase then ? I have seen a few threads with you looking at Planet X.
    I presume the bikes you are now looking at have a shorter TT than the Defy then.

    Yes. Ribble 872. 548mm vs 560 on the defy.
  • Avit5Avit5 Posts: 114
    Camcycle1974 wrote:
    Avit5 wrote:
    Camcycle - Have you decided on your next purchase then ? I have seen a few threads with you looking at Planet X.
    I presume the bikes you are now looking at have a shorter TT than the Defy then.

    Yes. Ribble 872. 548mm vs 560 on the defy.

    For me the R872 is too long top tube. My recommended size is 54.5 as per Ribble height sizing but the TT is 583 with a HT of 182. Great looking bike though and might look at the Sportive range they do as the geometry on them is more towards what I think I need.
  • Camcycle1974Camcycle1974 Posts: 1,356
    Avit5 wrote:
    Camcycle1974 wrote:
    Avit5 wrote:
    Camcycle - Have you decided on your next purchase then ? I have seen a few threads with you looking at Planet X.
    I presume the bikes you are now looking at have a shorter TT than the Defy then.

    Yes. Ribble 872. 548mm vs 560 on the defy.

    For me the R872 is too long top tube. My recommended size is 54.5 as per Ribble height sizing but the TT is 583 with a HT of 182. Great looking bike though and might look at the Sportive range they do as the geometry on them is more towards what I think I need.

    You must be pretty tall. Just under 5"10 and the 50 is the right size. The 54 should be big enough up to 6"3 or so.
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